1. Field of the Invention
The present invention relates to a scroll fluid machine capable of reducing wear of seal members that are provided between end plates and the distal end faces of wraps while ensuring a tight seal therebetween.
2. Description of the Related Art
Scroll expanders are known, which have a pair of scrolls each formed of an end plate and a spiral wrap provided to stand on the end plate, the end plate and wrap defining and forming a plurality of expansion chambers. The scroll expanders produce rotary torque by an expansive force of working medium that is supplied at high pressure into the expansion chambers. For example, Japanese Patent Application Laid-open No. 2006-46223 discloses a scroll expander having a fixed scroll fixed to a casing and a movable scroll that rotates eccentrically to the fixed scroll.
In this scroll expander, the movable scroll is attached eccentrically to a crankshaft, so that it orbits eccentrically to the crankshaft. The movable scroll is provided with an anti-rotation mechanism to stop it from rotating around its own axis. A refrigerant introduced into expansion chambers at high pressure as a working fluid pushes the movable scroll to rotate it eccentrically with an expansive force. As a result, the volume of the expansion chambers increases, with which the refrigerant undergoes expansion. The expanded refrigerant flows out from an outlet. The rotary motion of the movable scroll is provided as rotary torque via the crankshaft. In recent small power generation systems, scroll expanders are incorporated to use the rotary torque produced by the movable scroll for the power generation.
It is necessary to provide an airtight seal for the expansion chambers in a scroll expander, and the airtight condition of expansion chambers is kept by cutting a recessed groove in the distal end face of the wrap that makes sliding contact with an opposite end plate, and mounting a tip seal in this recessed groove. Similarly, in scroll compressors that form compression chambers with a pair of scrolls to produce compressed gas, scroll blowers, or vacuum pumps that use scroll compressors, a tip seal is mounted in the distal end face of a wrap that makes sliding contact with an opposite end plate to prevent leakage of compressed gas during the compression process.
For scroll compressors, means of causing the tip seal to make tight sliding contact with the opposite end plate has been proposed, wherein notches are formed by making cuts in a bottom or side face of the tip seal, and compressed gas is guided toward the notches, to increase the tightness of the seal between the opposite end plate and the tip seal. Another means of pressing the tip seal against the opposite end plate that has been proposed is an elastic member such as rubber, elastomer or the like inserted between the bottom face of the recessed groove and the bottom face of the tip seal to apply a pressing force.
Japanese Patent Application Laid-open No. H9-158853 discloses a scroll compressor provided with a tip seal that absorbs moisture supplied thereto and swells on the distal end faces of wraps. The tip seal absorbs moisture supplied from outside and swells, thereby being entirely pressed against the opposite end plate in uniform pressing force, so that the compression chambers are kept sealed.
Japanese Patent Application Laid-open No. 2006-97656 discloses a scroll compressor, wherein an elastic filling member is provided between side and bottom faces of a recessed groove and side and bottom faces of a tip seal to fill the gap between the recessed groove and tip seal, when mounting the tip seal in the recessed groove formed in the distal end face of the wrap. The compressed fluid is thereby prevented from leakage through the recessed groove.
Generally, air compressors employ an oil lubrication system, in which lubricating oil is supplied to the compression chambers for the purposes of preventing a temperature rise of compressed air or the like, sealing the compression chambers, and lubricating the sliding parts. Such oil-lubricated air compressors cannot be used in factories which require clean compressed air, for example, food factories, pharmaceutical factories, or precision equipment factories, because the oil component mixed in the compressed air cannot completely be removed. Therefore, water-lubricated air compressors have been proposed, which use water instead of lubricating oil. As such a water-lubricated air compressor generates oil-free compressed air, the compressor can be used even in a factory which requires clean compressed air. Japanese Patent Application Laid-open No. 2007-162484 discloses one such water-lubricated air compressor. The structure of the common water-lubricated air disclosed in Japanese Patent Application Laid-open No. 2007-162484 will be described below with reference to FIG. 7.
In FIG. 7, the water-lubricated air compressor 100 includes an basic air compressor 102 that compresses air, a separator tank 104 that separates water from the compressed air, a dryer 106 for removing moisture contained in the compressed air, and a water cooler 108 that cools the water. The basic air compressor 102 is configured by a compressor such as a scroll compressor, screw compressor, reciprocating compressor, or turbo compressor. Water supplied to the basic air compressor 102 from piping 110 is used for lubrication between scrolls and cooling of the scrolls in the case with a scroll compressor. Air to be compressed is supplied to the basic air compressor 102, where it is compressed, by opening a valve 114 in piping 112.
The compressed air travels through piping 116 with water to the separator tank 104, where it is separated from the water. As this air separated from water contains much moisture, it is dried by the dryer 106, and exits from a discharge pipe 118 to a user side. Water 120 separated in the separator tank 104 is supplied through piping 122 to the water cooler 108, where it is cooled. The water cooled in the water cooler 108 is supplied to the basic air compressor 102 through the piping 110.
When the water circulating in the water-lubricated air compressor 100 needs to be cleaned, a water discharge valve 124 is opened to discharge water in the separator tank 104 from piping 126 as required, while a water supply valve 128 or 130 is opened to supply fresh water from the piping 132 or 134. The water level inside the separator tank 104 is checked by means of a water gauge 136 provided in the separator tank 104.
In scroll expanders, as steam or refrigerant used as the working medium undergoes adiabatic expansion in the expansion chambers, the working medium or the steam contained therein condenses, whereby condensed liquid of working medium or condensed water is generated. Such condensed liquid or condensed water present between the opposite end plate and the tip seal provides a sealing effect for preventing leakage of the working medium from the expansion chambers. However, with such condensed liquid being present between the tip seal and the opposite end plate, if a pressing force is applied to press the tip seal against the opposite end plate and if the tip seal is kept in pressure contact with the opposite end plate, wear of the tip seal will progress because of the effect of the liquid.
In water-lubricated scroll compressors, too, the water used as the lubricating liquid present between the opposite end plate and the tip seal provides the sealing effect for preventing leakage of compressed gas from the compression chambers. However, as with scroll expanders, if a pressing force is applied to press the tip seal against the opposite end plate and if the tip seal is kept in pressure contact with the opposite end plate, wear of the tip seal will progress because of the effect of the water.
Therefore, the means of pressing the tip seal against the opposite end plate disclosed in Japanese Patent Application Laid-open No. H9-158853 cannot be employed in scroll expanders or water-lubricated scroll compressors for increasing the sealing effect. The means disclosed in Japanese Patent Application Laid-open No. 2006-97656 cannot resolve the problem of progressive wear of the tip seal noted above. On the other hand, the function of keeping the seal between the tip seal and the opposite end plate is required, in consideration of the loss of the sealing function of the tip seal due to the tolerance caused by processing errors, or thermal deformation during the operation, of components forming the expansion or compression chambers.